Atmospheric acoustics: A. Petculescu
As evidenced by recent missions such as Cassini-Huygens, Mars Phoenix, Venus Express, there is growing interest in detecting and analyzing signatures of wave motion in planetary atmospheres. At UL Lafayette, we are combining data analysis, theoretical and computational modeling to predict the characteristics of acoustic and gravity wave propagation in terrestrial atmospheres (Earth, Mars, Venus, and Titan). These studies are important in planetary science because they guide instrumentation development and data analysis. We have recently completed a study of the generation and propagation of thunder on Titan. The results, published here, show the optimum frequency bands in which future detectors should look. Limiting the working bandwidth helps save onboard power and optimize the measurement process.
- Infrasound absorption and dispersion in Earth's lower thermosphere (between 80 and 160 km). The premise of this project, whose preliminary results were published here, is that at thermospheric altitudes the molecular mean-free-path is large enough to require non-continuum fluid mechanics. Therefore, in our pilot study, we have developed a framework based on the Boltzmann transport equations whereby themal conduction and viscous stress are coupled. Furthermore, the lower thermosphere corresponds to the D and E ionospheric layers, for which reason, in the current project stage we include magnetohydrodynamics to treat the mixture of neutral and charged particles.
- Acoustic dispersion and absorption profiles in Venus' lower and middle atmospheres (0 to 100 km). Venus Express has shown evidence of distinct cold and warm layers in Venus' atmosphere, and has also probed the planet's polar vortex in detail. The measurements show a dynamic and yet mysterious environment. Acoustic measurements will help to better constrain the Venusian atmospheric dynamics, fluxes, as well as cloud composition. For instance, fast and robust active acoustic sensors based on molecular acoustics could help identify the mean molecular weight and the geometry of an unknown UV-absorbing molecule at around 50 km.
Condensed matter physics: G. Petculescu
We use ultrasonic techniques such as Resonant Ultrasound Spectroscopy (RUS) and pulse-echo to obtain information about lattice dynamics and physical properties such as elastic moduli and magnetoelastic constants of novel materials (elements, alloys, and compounds). To study the elastic properties of samples with varied geometries and under a range of conditions, we probe the structures with bulk, surface, and Lamb waves, in both the linear and nonlinear acoustic regimes.
A particular class of materials of current interest are Fe-Ga alloys (known as Galfenol). Their strong magnetostrictive coupling make them promising candidates as transducer materials, whether as precision drivers or energy-harvesting devices. Gabriela Petculescu is currently measuring the elastic properties of Fe-Ga alloys as a function of composition, over a range of temperatures and magnetic fields.
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Underwater acoustics: N. Sidorovskaia
Underwater acoustics is a research area where scientists collect acoustic signals produced by humans or nature in the ocean and decode them through sophisticated signal processing and interpretation techniques. Acoustic signals are the most viable sensing tools to explore the underwater world because, unlike electromagnetic signals, they can propagate far from the source. This fact explains why marine animals (dolphins, whales etc.) have the most advanced sound production and perception (hearing) organs.
Underwater acoustics research at UL Lafayette is concentrated on developing computational models to accurately predict how different sounds propagate through different regions of the ocean. These models are used in detailed mapping of ocean temperature (ocean acoustic tomography) which impacts hurricane strengths and paths; in seismic data interpretation to find oil/gas reserves for deep water drilling; and in predicting the human environmental impact on marine life. In the past decade she has been also closely involved in designing, conducting and processing passive acoustic experiments to study marine mammals, particularly sperm and beaked whales in the Gulf of Mexico.
In 2000 we formed a consortium of scientists called the Littoral Acoustic Demonstration Center (LADC). LADC research is mostly dedicated to studies of marine mammals in the world oceans based on recordings of their acoustic signals. One focus of LADC research is the search for subtle signatures in animal’s phonations that may give scientists clues how to recognize individual animals acoustically in collected data and to understand their communication codes (“languages”). The expertise of the LADC group has currently been acknowledged by awarding our consortium over $5,000,000 in funding from BP/GOMRI research program to continue monitoring effects of the 2010 Gulf of Mexico on deep diving marine mammals. This award will open unprecedented opportunity for our research group to complete the only long-term study of the oil spill impact on several species of deep diving marine mammals using acoustic methods.